During organogenesis the proper spacial and temporal development of the vasculature is of fundamental importance to normal organ morphogenesis. We have described the presence of biochemical factors in non-vascularizing tissues which prevent invasion of these tissues by capillary endothelial cells. The identification of these factors and their mode of action is an important element in the understanding of how a vasculature is acquired by some tissues and not by others. What characteristics of endothelial cells are necessary for invasion of a tissue? Are proteases involved in the erosion of the stroma of the tissues being invaded? What type of collagen and proteoglycans are synthesized by endothelial cells which then form their basement membrane? Do these products change with age and diseases? Our observations have indicated that bone formation from a cartilage anlagen does not require the intimate contact of the vasculature. Is the vasculature an integral component in the formation of other structures such as the palate? Is an aberrant vasculature a causative element in the etiology of cleft lip and palate? Using A/Jax mice as a model system for cleft lip and palate we should be able to define the role of the vasculature in normal and abnormal development of the palate. BIBLIOGRAPHIC REFERENCE: Surface associated and released protease activity of endothelial cells in culture. Nino Sorgente and Zoltan Tokes. J. Cell Biology 67: 412a Abstract No. 823 (1975).